This invention relates generally to duct fittings, and more particularly to a fitting for installation of a nipple from the exterior of a duct, and method of installing same.
Industries of all types use ducting to conduct gaseous fluids. These include process piping systems and fume exhaust systems for various industries including the semi-conductor, pharmaceutical, pulpit paper, metals mining, chemical processing, petrochemical and hazardous waste disposal industries. For conducting corrosive fumes and chemically active gases, stainless steel duct and pipe coated with chemically resistant material such as Teflon is often used.
Occasionally, it is desirable to install a nipple into the duct after the duct system is already connected and in place, for the purpose of extracting samples or inserting sensors into the fluid passing through the duct. This poses a formidable problem, since the fitting cannot be welded without destroying the integrity of the duct internal coating. In the past, it has been necessary to either crawl into the duct to insert a flanged nipple with sealing gasket from the inside through a hole in the duct, or to resort to various special fittings and methods to install the nipple from the outside of the duct.
A number of authors have suggested schemes for installing a nipple from the exterior of a duct, these being listed below as follows, which list is not all-inclusive.
It would be desirable to have a simple fitting for installation of a nipple from the exterior of a duct which is comprised of simple parts and which can be installed from the outside of the duct. It would also be desirable to provide an externally installable nipple, which is compatible with a stainless steel duct coated internally with a protective layer of Teflon.
Accordingly, one object of the present invention is to provide an improved fitting for installation of a nipple from the exterior of a duct.
Another object of the invention is to provide an improved method for installation of such a nipple through a round hole in the duct.
Briefly stated, the invention comprises a fitting for installation of a nipple from the exterior of a duct having a wall with an aperture therein for receiving a nipple comprising a nipple installation member having a hollow externally threaded nipple portion, a flange disposed on one end thereof and dimensioned so as to pass through the aperture, and an elongated handling stem extending from the other end of the nipple portion; a flexible cup seal washer having an outer dimension greater than that of the aperture and adapted to cooperate with the flange to seal the nipple portion in the aperture, the washer being sufficiently flexible and so dimensioned to enable passage over the elongated handling stem and through the aperture; and a nut with threads matching the externally threaded nipple portion, whereby the nipple portion may be installed from the exterior of the duct and the elongated handling stem then removed to provide a nipple sealed in the duct wall.
In its preferred form the nipple portion, flange and elongated handling stem comprise a single plastic member, wherein the elongated handling stem is a solid extension integral with the nipple portion and closing off one end of the nipple portion. The method includes the steps of inserting the flange and nipple portion through the aperture while holding the nipple installation member by the elongated handling stem from outside the duct, passing the flexible sealing washer around the stem and through the aperture, tightening the nut around the nipple portion to compress the washer between the duct wall and the flange to seal the nipple portion in the aperture, and removing the elongated stem member to provide a nipple in the duct wall.